1. Field of the Invention
This invention relates generally to pantograph jacks, and more particularly to a pantograph jack for lifting and lowering a vehicle chassis or the like.
2. Description of the Prior Art
Generally, in prior art pantograph jacks, a load mounting stand and a base suppport are maintained in parallel with each other at the time of lifting and lowering operations of the jack, and for this reason, the gear shaped portions are provided in opposing relation to each other for those ends of the left and right-hand arms which are pivoted to the load mounting stand as well as for those ends of the left and right-hand arms which are pivoted to the base support, with the aforementioned opposing gear shaped portions being in meshing engagement with each other, such that the rotating angles of the left and right-hand arms about their points pivoted to the load mounting stand and the base support may be equal.
Usually, however, the load acting on the load mounting stand has been both eccentric and inclined, and the greater the degree of eccentricity, the degree of inclined angles, or the amount of the load applied to the jack, the greater will be the pressure acting upon the contacting surfaces of the gear meshing portions.
Therefore, the pressure acting upon the gear portions should be minimized as much as possible, and, in addition, means for such pressure minimization should be as simple as possible.
However, with prior art pantograph jacks, the surfaces of the gear shaped portions of the arms in most cases have been provided simply as punched surfaces of a steel plate, such that for reducing the pressure upon the contacting surfaces, the thickness of the steel plate itself should be increased to an undesired degree. Another prior art attempt at a solution has been to separately prepare the gear shaped portions having a greater thickness, and then, secure such gear shaped portions to the tip portions of the arms.
In the former case, however, the entire thickness of the steel plate is increased to such a degree as to be less economical or to lead to an increase in weight, in the case where the arms have a U-shaped cross section. In the latter case, there results an increase in the degree of misalignment in the meshing portions as well as an increase in the number of parts required as well as in the necessary man-hours for assembly.